1. Field of the Invention
The present invention relates to a method and a system for providing microstructural information of a biological target, more particularly to a method and a system for providing microstructural information of a biological target obtained from a plurality of diffusion weighted magnetic resonance images corresponding to a specific area of the biological target.
2. Description of the Related Art
Magnetic resonance imaging (MRI) is a noninvasive imaging technique commonly used for visualizing internal structures in vivo. The MRI uses a magnetic field to polarize the spin of hydrogen atoms of water in the biological tissue, and also uses radio frequency pulse to induce its excitation so as to cause the hydrogen nuclei to produce echo detectable by a MRI scanner.
Since 70% of a human body is water, MRI is a suitable noninvasive method for detecting organs and tissues of the human body. One type of MRI techniques, named diffusion MRI, is able to detect the water diffusion pattern of a living tissue. Since diffusion directions of water molecules contained in the biological tissue are affected by the structure of the biological tissue, the diffusion directions of the water molecules can be used for determining microstructure of the biological tissue. There are two imaging methods related to diffusion MRI to model such diffusion pattern, i.e., diffusion spectrum imaging (DSI) and Q-ball imaging (QBI).
Regarding the DSI, a MRI device is used to obtain a plurality of diffusion weighted image signals in q-space from a biological target (such as a brain). The diffusion weighted image signals are processed based upon Fourier transform, normalization, and integration to obtain an orientation distribution function (ODF) capable of representing directions of the water molecules. The ODF provides information about directions of fibers in the biological target, and a plot of the ODF is shown in FIG. 1. A vector a in FIG. 1 is one of possible directions of the fibers in the biological target, and axes x and y define all of the possible directions of the fibers. A magnitude of the vector a is a function value of the ODF. In FIG. 1, the plot of the ODF extends along the axis y, and therefore, it can be determined that the fibers are arranged along the axis y. However, since the DSI method requires interpolation for obtaining the ODF, computation in the DSI method is relatively complicated and the information provided by the ODF is relatively inaccurate.
The QBI method uses Funk-Radon transformation of the diffusion weighted image signals associated with a particular spherical surface to obtain the ODF, and the ODF is then normalized. Although computation in the QBI method is relatively simpler than that of the DSI method, the QBI method cannot be applied to any kind of q-space sampling systems. Thus, application of the QBI is limited.